I will be investigating the completeness of all of these and mentioning them as appropriate when I submit the revision of this paper. (In retrospect, I should have waited a week after posting the preprint before submitting for formal review; but I was so scared of letting it brew for years, as we’re still doing with the Barosaurus preprint to our shame, that I submitted it immediately.)

So we probably have a larger number of complete or near-complete sauropod necks than the current draft of this paper suggests. But still very few in the scheme of things, and essentially none that aren’t distorted.

So I want to consider why we have such a poor fossil record of sauropod necks. All of the problems with sauropod neck preservation arise from the nature of the animals.

First, sauropods are big. This is a recipe for incompleteness of preservation. (It’s no accident that the most completely preserved specimens are of small individuals such as CM 11338, the cow-sized juvenile Camarasaurus lentus described by Gilmore, 1925). For an organism to be fossilised, the carcass has to be swiftly buried in mud, ash or some other substrate. This can happen relatively easily to small animals, such as the many finely preserved stinkin’ theropods from the Yixian Formation in China, but it’s virtually impossible with a large animal. Except in truly exceptional circumstances, sediments simply don’t get deposited quickly enough to cover a 25 meter, 20 tonne animal before it is broken apart by scavenging, decay and water transport.

Taylor 2015: Figure 5. Quarry map of Tendaguru Site S, Tanzania, showing incomplete and jumbled skeletons of Giraffatitan brancai specimens MB.R.2180 (the lectotype, formerly HMN SI) and MB.R.2181 (the paralectotype, formerly HMN SII). Anatomical identifications of SII are underlined. Elements of SI could not be identified with certainty. From Heinrich (1999: figure 16), redrawn from an original field sketch by Werner Janensch.

Secondly, even when complete sauropods are preserved, or at least complete necks, distortion of the preserved cervical vertebrae is almost inevitable because of their uniquely fragile construction. As in modern birds, the cervical vertebrae were lightened by extensive pneumatisation, so that they were more air than bone, with the air-space proportion typically in the region of 60–70% and sometimes reaching as high as 89%. While this construction enabled the vertebrae to withstand great stresses for a given mass of bone, it nevertheless left them prone to crushing, shearing and torsion when removed from their protective layer of soft tissue. For large cervicals in particular, the chance of the shape surviving through taphonomy, fossilisation and subsequent deformation would be tiny.

So I think we’re basically doomed never to have a really good sauropod neck skeleton.

Incidentally, I know you guys don’t generally stray into this topic, but this could be used as evidence against creationism. If there were thousands of tons of sediment being flung around in some global flooding event, one would expect more articulated sauropods and other large animals to be present in the fossil record.

Huh. That had never occurred to me, but it’s actually a pretty good point. I do occasionally get to talk to church groups about evolution (I am a Christian myself), and your point is one that I may well find myself using. Thank you.

Sauropod necks are a lot of material. It’s similar to the issue of why we don’t have that many complete dinosaur tails, a question David Hone has asked (or if he’s merely implied it). This has less, perhaps, to do with size than it does with range from the main body, as the distal extremities of splayed skeletons tend to become disarticulated (as in other long necked animals, in plesiosaur paddles, tails almost always missing their tips, sauropod heads, etc.).

But that’s to the question of preservation. You suggested in your preprint that the volume of a sauropod skeleton is a lot to cover, perhaps implying in your way that the absence of sauropod heads generally are due to non preservation of heads which might tend to lie on the bank our outside the debris flow that buried the rest of the skeleton, implying as it does that the major agent for differential preservation here of a giant carcass is that it’s giant, an argument to my knowledge that has little in the way of experimental support.

But other factors contribute to carcass separation, of all of which are apparent on the carcass itself. Bioturbation, scavenging, primary predator feeding, etc., may likely contribute to first order disarticulation prior to aquatic disarticulation – when it has an effect – and taphonomy of the carcass directly resulting in movement of the carcass as or prior to burial, such as the assumption of opisthotonic posture.

I am concerned over one bit, though, and that’s the nature of distortion. While taphonomic forces are at play, we make assumptions that most skeletal distortion is generally taphonomic. There are virtually no perfect skeletons. Ever. This itself should not be remarkable, but of course what may be remarkable is the surveying of the distortion. By measuring asymmetry, etc. Additionally and this is my primary concern, is that some asymmetry is natural. I don’t think there is a perfect left-right symmetry in any skeleton I’ve seen, when of a single individual, and especially never in a fossil one, and this includes when dealing with median elements, such as vertebrae. So even when you account for taphonomic distortion, then you may consider natural asymmetry.

The concern over distortion in a series of bones entirely filled with air but otherwise structurally sound and solid seems of limited concern unless it can be mechanistically quantified.

Thanks, Rutger, good suggestions. Euhelopus — probably good, I will check. Nigersaurus — who can tell? We still await a full description. Rutland Cetiosaurus — no, like most old sauropod specimens, it’s bits and pieces from here and there.

Who knows what the deal is with Jobaria? Sixteen years on from the woefully inadequate preliminary description in the footnotes of a Science paper, it remains essentially undescribed. Once more, Science is inimical to science.